The first aerogels were produced in the late 1920s by Samuel Kistler, an undergraduate instructor at the College of the Pacific in Stockton, California. There is conflicting information regarding the precise timing of, and his motivation for, producing them, but throughout the twenties Kistler had been working with supercritical fluids (high-pressure fluids on the point of boiling). Whether by design or by accident, Kistler found a way to remove the fluid from a wet silica gel, leaving behind its solid structure. In the early 1930s, Kistler continued his experiments with aerogels, studying some of their thermal and catalytic properties.
The first commercial aerogels were produced in 1942 by the Mosanto corporation, under the trade name Santocel. The process involved soaking a sodium silicate solution in sulfuric acid, then repeatedly washing it in alcohol before drying it at high pressure. Mosanto described the product as "a light, friable, slightly opalescent solid containing as much as 95 percent air volume. It is a very effective heat insulating material." Mosanto claimed to have produced aerogels with densities of 1.8 pounds per cubic foot (29 kg/m3), but their regular output was between three and five pounds per cubic foot (48 to 80 kg/m3).
Mosanto marketed Santocel mainly as a flatting agent for paints and varnishes. Its applications, though not numerous, were as varied as thermal insulation in household freezers and an ingredient in Napalm. Because of its high manufacturing cost, however, Mosanto discontinued aerogel production in 1970.
nterest in aerogels, and their very low thermal conductivity, increased in the 1980s as energy conservation became increasingly important. However, high production costs still prevent their widespread use.
